Wrinkling, laxity, and pigmentive changes are most prevalent in sun- exposed areas of skin during aging especially in persons of fair complexion. Although the exact biochemical events of these manifestations of photoaging are not known, they have been attributed to oxidation based on a free radical mechanism. The objective of this project is to investigate a novel marker of photooxidation in human skin called carboxymethyllysine (CML). CML is a modified oxidation product of lysine. Recent evidence suggests that a two carbon aldehyde (i.e., glyoxal) fragments from autoxidizing lipid which reacts, in turn, with the free epsilon amino group of lysine to form CML. CML is a major immunodominant epitope of proteins modified by advanced glycosylation endproducts (AGEs) which increase in skin during human aging. Uptake of AGE-proteins induces a host of biological responses which are involved in cytokine secretion, induction of intracellular stress, and altered chemotaxis. The net effects of these responses are inflammation and irritation. The hypothesis to be tested in the present research is that UV radiation will catalyze the formation of CML in skin via the precursor glyoxal and that dermal cells once exposed to this type of radiation will produce CML. This project has three specific aims: 1) to determine the mechanism of CML formation in experimental models of photooxidation; 2) to determine differences in human skin in CML levels of sun-exposed versus unexposed areas; and 3) to determine the effects of UV/Vis exposure of cultured cells on CML production. CML will be quantitated by HPLC in various incubation models consisting of protein and PUFA (polyunsat. fatty acid) exposed to UV light to determine the mechanism of the reaction and whether glyoxal is indeed the precursor of CML. Levels will be measured in skin biopsies from volunteers to determine whether CML increases in sun-exposed areas of the body. Levels will also be measured in various cultures of dermal cells such as reticular and papillary human skin fibroblasts and melanocytes exposed to UV radiation.